Relais board create garbage on LCD, but only when the relay output is connected

Hi guys,

I added a relay board with two relais on my mega board.
But after a while running the sketch I get a lot of garbage on my lcd screen.

After googling I find a lot information with solution with capacitors.
But i tried everything but nothing helps.

Only there is a strange thing.

If I disconnect the wires from the relais output then the lcd has no problems and the relais is clicking without problems. But when i connect a 230volt led indicator lamp and let the relais put that lamp on and off the problems with the lcd screen starts again

I put several capacitors over the lamp but still I get the garbage on my lcd screen.

Is there an easy fix or do I have to change the lamps for 12 volt and hope the problem is gone?

If you are using 230 volt AC, then capacitors won't do anything, and if too large of a value, will produce smoke!

Keep ALL the 230 volt wires as far away from all DC and signal wires as possible. If that is not possible, make them cross only at right angles.

Paul

alanso: After googling I find a lot information with solution with capacitors.

Sounds thoroughly random. Well done! :astonished:

OK, just try a 100 µF (electrolytic) capacitor connected directly across pins 1 and 2 of your LCD which I discover is a "2004" character LCD - though you cross-posted this and didn't bother to tell anything about what you are doing.

OK, just try a 100 µF (electrolytic) capacitor connected directly across pins 1 and 2 of your LCD

Did that with several values but nothing helps.

So I took out the 230volt lamps and use now 12volt lamps. Problem is solved.

Thanks for your replies.

gr. Alan

There are many factors involved, but “lead dress” is critical. I have sadly lost my nice library of “potted” (cut-and paste) explanations of this - will have to re-write it over time.

Hi, See THIS PAGE about this type of problem, You'll have it again sooner or later on some project. Better to design against it from the start...

terryking228: Hi, See THIS PAGE about this type of problem, You'll have it again sooner or later on some project. Better to design against it from the start...

Very nice article, I've bookmarked it.

Just two points I would pick with it:

  • When you refer to a "common ground point", this is a concept which - unfortunately - actually requires more detailed explanation. It is not necessarily the case that one single ground point is appropriate, nor is the negative of the power supply, that common point and there also needs to be a matching common (positive) supply point. My reference to "lead dress" stems from the consideration that pairing of power and of data connections is the more critical matter and ground routing is a consequential part of that.

  • When you offer the "External Power jack" as an option for powering an Arduino, you really need to emphasise that this is only appropriate for your enhanced "RoboRED" design and not for the original Arduinos. This is not a matter of self-advertising or self-aggrandisement, it is an important fact! :astonished:

Hi Paul,

Thanks for the suggestions...

I will make it clearer in my pages what the power considerations are for the regular UNO when using the external power jack.

Lets discuss the "Common Ground Point" issue more. There certainly are multiple levels of this when high-frequency signals are involved. Individual circuit boards will/should have their own ground plane. They in turn may plug into a backplane that has a ground plane. A large system may have a large backplane with multiple "ground" planes if the same backplane includes both high power boards and low-level analog circuits.

There may be large subassemblies (such as the device interface board for a chip tester) that have their own separated ground planes and very short signal leads. I have been the design lead on systems like that, with 2 rack-mounted computers plus a couple distributed microcontrollers and the XYZ control of the prober. Planning the "Ground Point" issue early-on is really important. It's easier when you are on a raised floor and you can run 3 inch wide copper strap :-)

Let's try to find a good explanation that will be most helpful to people here making typical one-Arduino 'systems' of some type. It those cases, assuming the mixture of Arduino and some high-power controlled devices, I think the negative/common point of the power supply/supplies is the best initial suggestion.

Maybe we should pick this up as a separate thread on Project Guidance? Hmmmmm.

What do you think about all this?

I bet a Mars Rover has this same problem.

But sooner or later there has to be a Common Ground Point.